This invention concerns central filtration apparatus supplying filtered coolant to a plurality of machine tools. Machine tools typically are supplied with a flow of machining coolant which is directed through nozzles at the cutting tools and machined parts to lubricate and cool the cutting tools as the machining process proceeds.
The filtration apparatus is provided to filter the returned coolant and supply an adequate flow to all of the machine tools at a proper pressure.
The used coolant drains down into an individual sump located beneath each machine tool, which is equipped with a float control and pump to pump the used coolant back through a common return pipe to the filtration apparatus.
The coolant also washes away cutting chips and other solid material generated by the machining process, such as grinding swarf. Coolant and entrained solids flowing through the return pipe must be under sufficient pressure in order to insure that a sufficient minimum flow velocity is maintained along the length of the return pipe such that the solids are carried along with the coolant in the return pipe. If the flow velocity is too low, the entrained solids may settle out and create blockages.
Different types of machining operations produce solids of different densities such that different minium velocities must be maintained according to the type of solids being generated.
Piping of different sizes and configurations used for the coolant return also affect the minimum flow velocities necessary. In large scale installations with large flow volumes and large diameter pipes, the losses are low such that it is easier to maintain sufficient velocities due to the mass of the flowing liquid. Sloping of the return piping may be adequate to maintain the proper velocities.
However, in smaller installations, particularly with multiple turns and other restrictions, maintaining sufficient flow velocities is more difficult due to the much higher losses.
Another complication, particularly in small installations, is the considerable variations in system operating conditions which occur, such as during start up and the substantial effects of having one or more machine tools not operating at any given time. There may occur system conditions where one or more the machine tools are not pumping any dirty coolant into the return so that sufficient coolant flow in the return is not present to maintain the required minimum velocity of the return flow.
While clean coolant could simply be directed into the return piping via a bypass connection to maintain the flow velocities above the minimum level required, this would increase the required capacity of the central filtration apparatus as a significant portion of the filtered coolant would not be available for use by the machine tools.
Also, if a large flow of clean coolant is diverted into the return piping, elevated pressures therein requires increased sump pump output since dirty coolant must be introduced into the return piping at an elevated pressure. Larger piping networks would also be necessitated, further increasing the cost of the installation.
In order to deal with these variable conditions, the practice has in the past typically been to collect the flow from all of the sumps in a large auxiliary tank, with a separate additional pump used to pump coolant collected in the auxiliary tank back to the filtration apparatus. This additional equipment is a significant part of the cost of the system, particularly as a back up pump is often specified to be available if the first pump fails in order to reach a higher operating reliability.
Accordingly, it is the object of the present invention to provide an arrangement for insuring minimum flow velocities in the return piping for machine tool coolant filtering systems where maintaining a minimum flow velocity is difficult, over a wide range of varying system operating conditions.
It is another object of the invention to provide such an arrangement which does not entail any increase in the capacity of the filtering apparatus or sump pump sizes and without requiring any additional tanks or pumps.